Various electro-optical systems have been developed for reading optical indicia, such as bar codes. A bar code is a coded pattern of graphical indicia comprised of a series of bars and spaces of varying widths, the bars and spaces having differing light reflecting characteristics. The pattern of the bars and spaces encode information. Systems that read and decode bar codes employing imaging systems are typically referred to as imaging-based bar code readers or bar code scanners.
Imaging systems include charge coupled device (CCD) arrays, complementary metal oxide semiconductor (CMOS) arrays, or other imaging pixel arrays having a plurality of photosensitive elements (photosensors) or pixels. An illumination system comprising light emitting diodes (LEDs) or other light source directs illumination toward a target object, e.g., a target bar code. Light reflected from the target bar code is focused through a lens of the imaging system onto the pixel array. Thus, an image of a field of view of the focusing lens is focused on the pixel array. Periodically, the pixels of the array are sequentially read out generating an analog signal representative of a captured image frame. The analog signal is amplified by a gain factor and the amplified analog signal is digitized by an analog-to-digital converter. Decoding circuitry of the imaging system processes the digitized signals representative of the captured image frame and attempts to decode the imaged bar code.
Decoding an imaged bar code requires the decoding circuitry to identify the imaged bar code within a captured image frame. The more quickly the imaged bar code can be located within an image frame, the more quickly the decoding circuitry can operate on the appropriate portions of the image frame to decode the imaged bar code. Decreasing the time required to read, that is, to image and decode a target bar code, is of paramount importance to designers of bar code readers. Thus, methods that decrease, on the average, the time required to locate an imaged bar code in a captured data frame are of great interest.
Complicating the problem of efficiently locating an imaged bar code within a captured image frame is the fact that some imaging-based bar code readers are used in two different modes of operation, hand-held and fixed position. In the hand-held mode of operation, a user moves the reader housing with respect to a target bar code to “aim” the imaging system of the reader at a target bar code. This is sometimes referred to as the point-and-shoot mode of operation. Here the reader is moved and the item to which the bar code is affixed is typically in a fixed position or relatively fixed position. In the fixed position mode of operation, the bar code reader is fixed position, i.e., the reader housing is positioned on a sales counter, and the object that the target bar code is affixed to is moved by the user toward the reader such that the target bar code is brought within a field of view of the fixed position reader.
Unfortunately, it has been found that a method of locating an imaged bar code within a captured image frame that may be efficient for one mode of reader operation may not be as efficient for locating an imaged bar code in the other mode of reader operation. What is needed is a method of locating an imaged bar code within a captured image frame that is efficient for both modes of operation of an imaging-based bar code reader